Oxidative phosphorylation

Definition:

Process occurring in the cell, which produces energy and synthesizes ATP
(energy carrier of the body).

Source: GreenFacts

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Oxidative phosphorylation is a biochemical process in cells. It is the final
metabolic pathway of cellular respiration, after glycolysis and the citric acid
cycle. 26 of the total 30 ATP (energy carrier) molecules generated from a single
glucose molecule during cellular respiration come from oxidative
phosphorylation.

The process takes place at a biological membrane. In prokaryotes this is the
plasma membrane, and in eukaryotes it is the inner of the two mitochondrial
membranes. NADH and FADH2, electron carrier molecules that were "loaded" during
the citric acid cycle, are used in an intricate mechanism (involving NADH-Q
reductase, cytochrome c oxidase, and cytochrome reductase) to pump H+ across the
membrane against a proton gradient.

A large protein complex called ATP synthase is embedded in that membrane and
enables protons to pass through in both directions; it generates ATP when the
proton moves with (down) the gradient, and it costs ATP to pump a proton against
(up) the gradient. Because protons have already been pumped into the
intermembrane space against the gradient, they now can flow back into the
mitochondrial matrix via the ATP synthase, generating ATP in the process. The
reaction is: ADP3- + H+ + Pi -> ATP4- +
H2O